Project Summary/Abstract Multiple co-occurring chronic diseases (multimorbidity) among older adults are highly prevalent, disabling, and costly. Greater awareness of the complex interactions between diseases motivates the proposed project aims to identify disease combinations that drive important health outcomes such as disability, health-related quality of life, and mortality for vulnerable older adults. The proposed work will add to our understanding of multimorbidity combinations and their role in the development of disability in important ways by: (1) providing direct comparisons of prevalent multimorbidity groups for diverse elders, (2) quantifying the association between multimorbidity combinations and disability onset, and (3) identifying the changing care needs and health care expenditures of older adults with multimorbidity. The proposed work will provide important insights on which disease combinations pose the greatest risks for disability onset, which in turn may lead to loss of independence, institutionalization, and premature death. While our preliminary work finds that greater multimorbidity burdens accrue to older African Americans, and examines which diseases comprise the most frequently occurring multimorbidity combinations among older Americans, our proposed research enables the study of long-term influences of multimorbidity in over 20 years of nationally-representative biennial data (~37,000 people in the Health & Retirement Study), and 5 years of annual data (~8,000 people in the National Health & Aging Trends Study). We propose three aims: Aim 1. Determine the longitudinal development and progression of multimorbidity among older adults. Aim 2. Determine the onset of and changes in disability for older adults with multimorbidity. Aim 3. Evaluate changes in health care and mortality for older adults with varying multimorbidity and disability profiles.